The present invention relates to a process for preparing xcex1-hydroxyketones, namely 3-hydroxy-5-methyl-hexan-2-one and mixtures of this compound, with 2-hydroxy-5-methyl-hexan-3-one.
The skilled person in the food and beverage industry knows of the critical role flavor plays in the appreciation of food and beverage. Many food products, such as cocoa, chocolate, coffee, caramel, nuts, malt and the like have flavor quality that is referred to in the language of this art as xe2x80x9croasted brown.xe2x80x9d For purposes of the present invention, the term xe2x80x9croasted brownxe2x80x9d will be used to describe flavor properties of the mentioned food products, as well as of food products having similar flavor characteristics. As used herein, the term xe2x80x9cflavorxe2x80x9d is intended to mean flavor, aroma and/or taste.
From the above group of food products, flavor is especially important for chocolate. Fine flavor, high nutritional value, pleasing appearance and good storage qualities make chocolate a food product of exceptional value which is very popular and widely used. The flavor of chocolate depends on the quality and origin of the cocoa beans, on the processing thereof and the preparation of the chocolate. The processing steps which influence the chocolate quality include fermentation, drying, roasting, cleaning and milling of the cocoa beans. In the preparation of chocolate, the ratio of cocoa mass, sugar and cocoa butter, etc. determines the flavor of the product. The flavor of chocolate has been thoroughly investigated and many volatiles contributing to the overall flavor have been determined (I. Flament, xe2x80x9cCoffee, cacao and tea in volatile compounds in foods and beverages,xe2x80x9d H. Maarse, Ed., Marcel Dekker, Inc. New York, 1991; Grosch, Lehrbuch der Lebensmittelchemie, 4. Ed. 1997). Compounds mainly contributing to the cocoa flavor are aldehydes, especially isovaleraldehyde and phenylethanal, as well as the corresponding aldol condensation product 5-methyl-2-phenyl-2-hexenal.
Many chocolate and cocoa based foods and beverages produced by the food industry lack flavor characteristics of high quality chocolate and cocoa. A great deal of effort has been expanded to provide compounds with a natural chocolate or cocoa flavor for imparting the flavor of high quality chocolate and cocoa to products of low quality. U.S. Pat. No. 3,582,360 reportedly discloses unsaturated aldehydes, especially 2-phenyl-2-alkenals, for preparing flavor compositions and food products, particularly with chocolate and cocoa flavor.
Also, other food products with roasted brown flavor lack this freshly processed flavor. This short coming substantially reduces the overall organoleptic impression of the freshly roasted product. The missing flavor note is described as green, pungent and cocoa-like. The deficiency in roasted brown flavor is mainly due to a decrease of isovaleraldehyde. Isovaleraldehyde is relatively highly volatile, has a high reactivity towards alcohols, such as propylene glycol used as solvent in the flavorings, and undergoes aldol reactions with other aldehydes, such as phenylethanal, present in the flavorings.
The xcex1-hydroxyketones are another example of a flavorant. xcex1-hydroxyketones are reportedly well represented in food products. One example is acetoin (3-hydroxy-2-butanone) which has a buttery, creamy character and which can be found in a great number of food products (Volatile compounds in food, qualitative and quantitative data, TNO Nutrition and Food Research, supplement 5, H. Maarse, C. A. Visscher, L. C. Willemsens, L. M. Nijssen, M. H. Boelens, Eds., 1994). The compound 3-hydroxy-5-methyl-2-hexanone was reportedly found in water buffalo milk and its odor (GC sniffing) was described as similar to melted cheese (L. Moio, E. Semon, J. L. Le Quere, Ital. J. Food Sci. (1994), 4, 441).
The literature reportedly describes different methods for producing xcex1-hydroxyketones. For example, JP-A2-04120043 reportedly discloses the synthesis of xcex1-hydroxyketones by oxidizing olefins with H2O2 under acidic conditions. EP-A1-0 482 834 reports the preparation of xcex1-hydroxyketones by oxidizing olefins with peracetic acids in the presence of an Ru catalyst. JP-A2-03167150 reportedly describes the synthesis of xcex1-hydroxyketones by oxidation of alkynes with oxygen in the presence of silanes and a Co catalyst. JP-86-150522 reportedly describes hydrolysis of xcex1-halo arylketones in the presence of alkalihydroxides to prepare xcex1-hydroxarylketones.
From the discussion above, it is clear that there is a need for compounds which can be incorporated into, e.g., food and beverage products to impart roasted brown flavor thereto.
Accordingly, one object of the present invention is to provide a process for preparing compounds which are useful in imparting roasted brown flavor to food and beverage products.
Another object of the invention is a process for producing novel xcex1-hydroxyketones.
These and other objects of the invention will become apparent from the disclosure and claims set forth herein.
The present invention provides an economic process for preparing an xcex1-hydroxyketone. This process includes reacting 5-methyl-2-hexanone with sulfuryl chloride to produce 3-chloro-5-methyl-2-hexanone; forming 3-acetoxy ketone from 3-chloro-5-methyl-2-hexanone; and hydrolyzing the 3-acetoxyketone to form one or more xcex1-hydroxyketones.
It has now been found that roasted brown flavor can be imparted to, e.g., food and beverage products by including the novel compound of formula (I) set forth below: 
In another embodiment of the present invention, it has been found that a novel mixture of the compound of formula (I) with a compound of formula (II): 
imparts a similar sensory flavor impression to isovaleraldehyde of roasted brown flavorings, food products and beverages.
These new compounds and mixtures are especially useful for enhancing the flavor of flavoring compositions and food and beverage products with roasted brown flavoring characteristics.
As used herein, 2-hydroxy-5-methyl-3-hexanone is used interchangeably with 2-hydroxy-5-methyl-hexan-3-one. Similarly, 3-hydroxy-5-methyl-2-hexanone is used interchangeably with 3-hydroxy-5-methylhexan-2-one.
It also has been found that the two hydroxyketones (formulas (I) and (II)) of the present invention have a green, pungent, roasted and cocoa-like flavor. Mixtures of these hydroxyketones impart the pungent, cocoa-like note of isovaleraldehyde to chocolate, cocoa and other products with roasted brown flavor. Therefore, the hydroxyketones of the present invention are useful for enhancing or modifying the flavor profile of roasted brown flavors like cocoa, chocolate, coffee, caramel, toffee, roasted and regular nuts, such as for example, hazelnuts, almonds, walnuts, chestnuts, macadamia, coconut, roasted butter, condensed milk, malt and the like. The compounds of the invention are especially useful to enhance the powdery and cocoa-like notes of cocoa and other roasted brown flavor notes.
Flavoring compositions with the roasted brown flavor profile enhanced or modified with the hydroxyketones of the present invention are useful to impart freshly processed brown flavor qualities to food and beverage dairy products, such as, for example, UHT milk, condensed milk, yogurt, cream desserts, cheese, bakery products such as bread, biscuits, cookies, cakes, crackers, cereals and confectionery products, such as, for example, chocolate assortments, caramels, toffees and butterscotch.
Further, it has been found that the hydroxyketones of the present invention also act as masking agents in soybean derived products; while at the same time enhancing the flavor quality of these products. Soybean products like soybean milk, soybean yogurt, tofu, etc. have a cereal and nut-like character, i.e. such foods are accompanied by a typical green vegetable note.
Many consumers consider the green vegetable note as a drawback. Therefore, a masking agent for this typical green vegetable note in soybean products is of great value for the industry. The undesirable green vegetable and beany off-flavor of soy protein has been reduced by treatment with porcine liver aldehyde oxidase (P. Maheshwari, P. A. Murphy, Z. L. Nikolov, J. Agric. Food Chem. 1997, 45, 2488), by treatment with liquid and supercritical carbon dioxide (P. Maheshwari, E. T. Ooi, Z. L. Nikolov, J. Am. Oil Chem. Soc. 1995, 72, 1107) and by fermentation with Bacillus subtilis and Bacillus natto (S. H. Choi, Y. A. Ji, Korean J. Food Sci. Technol. 1989, 21, 229).
Surprisingly, by the addition of the hydroxyketones of the present invention, not only are the undesirable green vegetable and beany notes of soybean products remarkably reduced, but at the same time, the cereal nutty characteristics are enhanced. This results in a product with a more overall accepted flavor profile that is no longer associated with the negative green vegetable flavor of soybean derived products.
The compounds of the present invention are also useful when combined in food and beverages having other flavor characteristics, such as fruit products, diary products, vegetable products, meat products, spices, herbs, pharmaceutical products and oral hygiene products and the like.
The hydroxyketones of the present invention, for example, can be incorporated into a product, such as a flavor composition including the usual additives known to those skilled in the art. When the hydroxyketones of the present invention are used in flavoring compositions to enhance, modify or mask existing flavors or to provide a characteristic impression, they may be incorporated into the flavoring compositions alone or in combination with additional flavor ingredients used for food products.
Additional flavoring ingredients which create roasted brown flavorings to be added to the above-referenced flavor composition include esters, aldehydes, ketones, alcohols, lactones, heterocycles, such as for example, furans, pyridines, pyrazines and sulfur compounds, such as for example, thiols, sulfides, disulfides, and the like. These components can be combined in proportions normally used in the art for the preparation of such flavoring compositions.
When the hydroxyketones of the present invention are used in flavoring compositions having a roasted brown flavor profile, to provide or modify the characteristic impression of isovaleraldehyde, especially as in cocoa and chocolate flavoring compositions, they may be combined with isovaleraldehyde. Isovaleraldehyde, usually present in chocolate, cocoa and other flavorings can be partially or completely substituted by the hydroxyketones of the invention. The combination of the compounds of the present invention with isovaleraldehyde is preferred for cocoa and chocolate flavoring compositions because of their milk chocolate-like flavor.
The amount of hydroxyketone(s) of the present invention used in the various compositions described herein depends on the precise organoleptic character desired in the finished product. For example, in the case of flavoring compositions, the amount of hydroxyketone(s) of the present invention incorporated therein will vary according to the food or beverage in which the flavor has to be enhanced or modified. The amount of hydroxyketone(s) of the invention incorporated into the flavoring will also depend on whether the roasted brown flavor profile of a product has to be enhanced or modified; or whether a full rounded roasted brown flavor has to be imparted to an unflavored material.
In the later case, more of the hydroxyketone compound(s) of the invention are required. For example, a ready-to-consume product with a roasted brown flavor preferably contains at least about 1 ppm of a hydroxyketone of the present invention based on the total weight of the product. It is generally desirable not to use more than about 20 ppm in the ready to consume product. The desirable range of the flavoring composition in the ready to consume product corresponds to about 3 to about 6 ppm of a hydroxyketone of the present invention. The amount of the flavoring composition added to the product should not only impart the desired flavor to the product, but it should also give a balanced impression. Accordingly, a flavoring composition of the present invention preferably contains about 0.5% to about 1% of a mixture of hydroxyketones of formula (I) and (II) based on the total weight of the flavoring composition.
In the present invention, the ratio of 3-hydroxy-5-methyl-hexan-2-one to 2-hydroxy-5-methyl-hexan-3-one can vary from about 1:1 to about 99:1.
For soybean products, it is preferable to add at least about 0.1 ppm of a hydroxyketone of the present invention, based on the total weight of the product. An upper limit of 20 ppm of a hydroxyketone of the present invention based on the total weight of the product is preferred. Flavor compositions for masking the undesired soybean flavor contain preferably about 0.5% to about 1% of a hydroxyketone of the present invention based on the total weight of the flavoring composition.
It may be desirable in the flavoring compositions of the present invention to incorporate flavor delivery vehicles or carriers, such as, for example, gum arabic, maltodextrin, etc., or solvents such as ethanol, propyleneglycol, water, triacetin, etc. When the carrier is an emulsion, the flavoring composition may also contain emulsifiers such as mono- and diglycerides of fatty acids and the like. By using such carriers or solvents, the desired physical form of the flavoring composition can be obtained. The flavoring compositions of the present invention can take various forms, including for example, spray-dried, liquid, encapsulated, emulsified or other forms.
The flavoring compositions of the present invention can be added to food and beverage by conventional methods known to the skilled person. For example, a chocolate praline may be prepared by incorporating into the flavoring composition fat, sugar, milk, cocoa powder and stabilizers and admixing of these ingredients in a conventional freezer. A powdered chocolate or cocoa mix may be prepared by admixing dried milk solids, sugar and the flavoring composition in a dry blender until uniformity is obtained. When such dry mixtures are used, the hydroxyketones or flavoring compositions of the present invention can be added to one or more of the solid ingredients or to any portion thereof. In this case, the flavoring composition may be spray-dried, encapsulated or the like.
The process for preparing the xcex1-hydroxyketones of the invention starts from inexpensive 5-methyl-2-hexanone which is reacted with sulfuryl chloride in a first step to give 3-chloro-5-methyl-2-hexanone with high selectivity, as set forth below: 
The 3-chloro-5-methyl-hexanone is treated in a second step with potassium acetate and alkali iodide: 
The 3-acetoxy-ketone, e.g., 3-acetoxy-5-methyl-2-hexanone obtained in the second step is hydrolyzed under alkaline conditions to give the desired 3-hydroxy-5-methyl-2-hexanone or a mixture of 3-hydroxy-5-methyl-2-hexanone and 2-hydroxy-5-methyl-3-hexanone.
The first step of the above synthesis is performed in the presence or absence of an inert solvent such as hexane, cyclohexane, benzene, toluene and the like. Hexane is preferred. The reaction is carried out between room temperature and reflux temperature, the latter being preferred.
The molar ratio of 5-methyl-2-hexanone to sulfuryl chloride may vary from about 1:1 to about 1:1.5, preferably about 1:1.2. Molar ratios of 5-methyl-2-hexanone to sulfuryl chloride below about 1.2 result in less chloroketone containing minor amounts of 3,3-dichloroketone. Molar ratios of 5-methyl-2-hexanone to sulfuryl chloride higher than 1.2 result in higher yields of chloroketone, however, formation of 3,3-dichloroketone increases. The product may be purified by distillation or directly used in the following step.
In the second step of the process according to the present invention, the 3-chloro-5-methyl-hexanone is treated with potassium acetate and an alkali iodide in an inert solvent, such as tetrahydrofuran, acetonitrile, methylvinylketone, diethylketone, acetone and the like. The reaction is preferably run in acetone at the reflux temperature. Per mol potassium acetate is 1:10 mol%, preferably 4 mol% of alkali iodide is used. Sodium iodide is preferred. The reaction mixture may be hydrolyzed with water or preferably is filtered to remove insoluble salts and washed with water and a sodium thiosulfate solution to remove traces of iodine. The crude product is purified by distillation under reduced pressure.
The 3-acetoxy-5-methyl-2-hexanone obtained in the second step of the process is hydrolyzed in the third step with an aqueous alkaline solution to give the desired 3-hydroxy-5-methyl-2-hexanone or mixtures of 3-hydroxy-5-methyl-2-hexanone and 2-hydroxy-5-methyl-3-hexanone. The hydrolysis is carried out between 0xc2x0 C. and reflux temperature depending on the desired ratio of isomeric hydroxyketones of formula (I) and (II). Preferably, the reaction is run at low temperature, i.e., closer to 0xc2x0 C. than the reflux temperature, with a short reaction time using weak alkaline solution with a molar ratio of a base to acetoxyketone of about 1.1 to about 1. These conditions yield 3-hydroxy-5-methyl-2-hexanone of high isomeric purity.
If the reaction is run at elevated temperature and for a long reaction time using a strong alkaline solution with a molar ratio of about 10 mol of base per mol acetoxyketone, an isomeric mixture containing approximately equal amounts of 3-hydroxy-5-methyl-2-hexanone and 2-hydroxy-5-methyl-3-hexanone is obtained. Using a weak alkaline solution and a long reaction time with a molar ratio of the base to acetoxyketone of about 1.1 to about 1 results in a mixture containing a higher amount of 3-hydroxy-5-methyl-2-hexanone.